Electric switch



April 15, 1941. A. BLAIN ELECTRIC SWITCH Filed July 50, 1938 (/ll/ I d'ttorneg Patented Apr. 15, 1941 ELECTRIC SWITCH Albert Blain, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Dela- Application July 30, 1938, Serial No. 222,082

1 Claim.

This invention relates to switches, particularly to intermittently actuated electn'c switches and has special reference to the provision of improvements in switches of a type adapted to produce framing or synchronizing impulses in facsimile and other systems for the communication of intelligence.

In transmitting a picture by radio or by wire, a change from a given standard in the marginal or in the over-all dimensions of the picture requires changes in the duration of the accompanying framing or synchronizing impulses. Such changes have heretofore been accompanied by means of a switch operated by a mechanism which included one or more interchangeable or adjustable cams. Interchangeable cams have proven objectionable because it is not always practical to anticipate the relative duration of the timing impulses each picture will require in its transmission. Adjustable cams, like interchangeable cams, require stoppage of the transmitter during their adjustment and, further, are difficult to adjust.

Accordingly, the principal object of the present invention is to provide a simple, inexpensive and trouble-free intermittently actuated switch, and one capable of being readily adjusted to control the length or percentage of time the switch is in the closed or open position during each cycle of the actuating mechanism.

Other objects and advantages, together with certain details of construction, will be apparent and the invention itself will be best understood by reference to the following specification and. to the accompanying drawing, wherein Figure l is a side elevational view of an adjustable intermittently-actuated switch constructed in accordance with the principle of the invention and including a motor and shaft for applying an operating force to the switch,

Figures 2, 3 and 4 are sectional views taken on the line 2--2 of Fig. 1 and show the adjustable member to which the operating force is applied in various operating positions, and

Figure 5 is a sectional view of a modified form of cam surface for use in conjunction with the switch actuating member of Figs. 1 to 4, inclusive.

In Figs. 1 to 5, inclusive, l designates a shaft adapted to be rotated as by a constant speed motor 2 (Fig. 1) and to which a rotatable member 3 is affixed as by a hub 4. Shaft I may comprise a support for a scanning drum, not shown, when the invention is applied to a facsimile transmitter or receiver. The rotatable member 3 is preferably in the form of a circular disc or plate and is provided, on one of its major surfaces 3 with a bevelled cam surface which may be in the form of a detent 3 which extends outwardly from the axis 1. v

A switch 5 which may comprise a pair of fixed contacts 6, l and a switch actuating member in the form of a movable contact 8 is mounted for pivotal movement tangent to the axis l on a suitable support 9 as by means of a set screw Ill. The switch actuating member or arm 8 is provided at its free end with an insulating portion 8 which is maintained in contact with the face of the rotatable member 3 by the biasing force exerted by the spring portion of the arm. As the shaft l and disc 3 are rotated by the motor 2 the switch actuating member 8 will be urged against one or the other of the switch contacts 6, l as determined by the instantaneous position of the insulated terminal 8 with respect to the plane surface (i and cam surface 3 of the disc.

When the bevelled long edges of the detent 3 are parallel, the portion of each cycle of the retating member 3 during which the switch arm 8 is maintained against thecontact 6 is determined by the distance between the axis of the shaft I relatively longer period of time than it will be when the arm is in the upright position, shown in Fig. 2. Similarly, when the switch is inclined outwardly, toward the periphery of the disc, as shown in Fig. 4, contact 6 will be closed during a smaller part of each cycle than it is when the switch arm is adjusted to either of the positions shown in Figs. 2 or 3.

In order to provide a greater range of adjustment, the cam surfaces 3 and 3 may assume various forms. Thus, referring to Fig. 5, the detent, here designated I3 may be formed with edges which converge in the direction of the periphery of the disc, whereby the period of time during which the switch arm is in contact with this cam surface, during each revolution of the rotatable member, is disproportionately less when the said arm is adjacent the periphery than when it is adjacent the axis of the rotatable member.

Other modifications of the invention will suggest themselves to those skilled in the art. It is to be understood therefore that the foregoing is to be interpreted as illustrative and not in a limiting sense, except as required by the prior art and the spirit of the appended claim.

What is claimed is:

In combination, a rotatable member having an aXis and a, surface having a 'detent therein comprising a cam which extends outwardly from said axis, a switch comprising a plurality of contacts remote from said rotatable member and an actuating member for said remote contacts mounted tangent to the axis of said rotatable member and biased to engage said cam surface, and means for moving said switch actuating member radially with respect to said axis whereby to regulate the period of time during which said switch actuating member is in contact with said cam during each revolution of said rotatable member, said switch contacts being biased to close when said switch actuating member engages said cam.

ALBERT BLAIN. 

